As an image forming apparatus such as a color copying machine or a color printer, there is an apparatus that converts plural colors determined as difficult for color weakness people, who have color sense characteristics different from a general color sense, to distinguish into the same colors in a color space of data for image formation. However, the color sense characteristics of the color weakness people are not uniform and are different for the respective color weakness people. Therefore, simply by converting the specific plural colors determined as difficult to distinguish into the same colors, images having tints easy to see for the color weakness people are not always obtained according to the color sense characteristics of the respective color weakness people. Further, it is likely that images having tints corresponding to tastes of the respective color weakness people are not obtained.